This invention relates to acoustical devices and methods, and to the manipulation of acoustical energy. More particularly, the invention relates to a SASER (Sound Amplification by the Stimulated Emission of Radiation), the acoustic analogue of the laser. The method and apparatus of the invention enable the directional emission of amplified, coherent sound waves.
The fundamentals of acoustics, sometimes referred to as vibrational energy, have long been studied and understood. At its simplest, the field of acoustics concerns the propagation through a medium of a series of pressure waves. The wavelength, frequency, and speed of the waves can be measured and correlated. The most familiar form of acoustic energy to humans is perceived sound. The term in general, and specifically as used herein, however, refers to the entire spectrum of this type of energy.
Acoustics, especially at ultrasonic frequencies, are finding an increased number of uses in a widening array of fields. Ultrasonic devices are used for cleaning, such as removing scale or other contamination from surfaces. Ultrasound is also being used to effect certain chemical processes in a field sometimes referred to as sonochemistry.
A method of using ultrasonic energy for separating the constituents of a mixture, referred to as acoustophoresis, is set forth in U.S. Pat. No. 5,192,450, issued to Heyman. According to the disclosure, an acoustic wave is transmitted at one end of a container to a sample therein via a transducer at ultrasonic frequencies. The wave can be xe2x80x9ctunedxe2x80x9d to the resonance of a desired constituent, forcing the constituent to one end of the container for separation. This methodology requires that the acoustic wave be propagated throughout the container, requiring either a relatively small sample size or prohibitive amounts of energy.
Separation using ultrasonic means is also the subject of U.S. Pat. No. 4,983,189, issued to Peterson et al. The discussion and disclosure therein concerns the use of ultrasonic frequencies to establish standing waves in a medium. Particles in the medium, depending on a number of characteristics such as resonance, size, and composition, will migrate toward the regions of highest pressure in the standing wave or to the regions of lowest pressure in the standing wave. In standard nomenclature, adopted herein, a region of high pressure is termed an antinode and a region of low pressure is termed a node. This separation technique, sometimes also called acoustophoresis, requires that the entirety of the sample be subject to the standing wave, or waves, to effect separation. Again, this limits the method to relatively small sample sizes or large expenditures of power.
A fairly common use of ultrasonic energy is cleaning surfaces. It is believed that the cleaning is accomplished largely through a process known as cavitation. Cavitation is the creation and rapid collapse of relatively small voids in a medium subjected to acoustic energy at ultrasonic frequencies. While not all aspects of cavitation are fully understood, it is believed that this phenomenon causes extremely high and transient temperatures and pressures. An intense, highly localized, shock wave is also created.
These effects, although occurring over only a very small area for each void created and destroyed, can be very destructive. Cavitation is therefore a very useful way to clean a relatively hard surface of such accretions as scale and alga without damaging the surface. Because acoustic energy can essentially permeate a medium, the technique is also useful for surfaces which because of size, location, or intricacy are difficult to reach.
One prior art device that can be used for cleaning surfaces is disclosed in U.S. Pat. No. 4,691,724 to Garcia et al. This patent discloses a probe which can be lowered into a medium. The intention can either be to clean the surfaces of the vessel containing the medium, or to clean objects within the vessel. Garcia et al. describe a means by which both longitudinal and radial waves can be generated by the probe. The probe contains a piezoceramic transducer, which vibrates in response to input from a tunable power source to produce ultrasonic waves in the medium.
Generating controlled radial and longitudinal waves, according to the disclosure, produces surface-cleaning cavitation more efficiently and throughout a greater volume of medium. With this device also, the entire medium must be permeated, especially to reach and clean the walls enclosing the medium. The radial waves at least are generated omnidirectionally around the circumference of the probe such that for any given surface area, only a fraction of the energy input is effective at that area.
In recent years, theoretical attention has been paid to the physics of a SASER, the acoustic equivalent of the well-known laser. The known literature, however, does not disclose a functional, practicable apparatus or method of embodying the proposed physics. Such an apparatus and method, useful for solving the problems with existing acoustic equipment as set forth above, has thus been long-sought in the art.
It is an object of this invention to provide an apparatus and a method for concentrating acoustic energy and emitting it as a narrow beam of single frequency sound waves.
It is another object of this invention to provide an apparatus and method for greatly increasing the efficiency of the transduction of electrical energy to acoustic energy.
It is a further object of this invention to provide an acoustic laser, or SASER, capable of emitting concentrated pressure waves at a single frequency into a medium.
It is yet another object of this invention to provide a highly efficient means of projecting directional sound waves into and through a suitable medium.
It is still another object of this invention to provide a means for inducing cavitation within a medium along a specified path or at a specified location.
These and other objectives are achieved by means of an acoustic apparatus having a housing having an opening, a hollow cylindrical transducer mounted in the housing, the transducer having a first and a second end, the first end of the transducer being aligned with the opening in the housing and the second end being closed by a rigid wall, an acoustically conductive active medium filling said transducer, and a power supply operatively connected to the transducer capable of exciting the transducer to produce acoustical energy in the active medium.